Maybe i should clarify my inquiries first... It is about whether freelist refilling will trigger any tree splits or even tree growths in by-size freespace tree. When reading the source code of XFS(xfs_alloc.c) to find information about freelist refilling in xfs_free_extent(), I found that insertion to by-block B+ Tree is not possible to happen since there is only record updates in this tree. That sounds clear to me. But insertion to by-size B+ Tree may happen in xfs_alloc_fixup_trees() after removing an record from the tree. Thus I come up with a doubt. Is tree split or tree growth in by-size B+ Tree possible in the above case? On Thu, Jul 7, 2016 at 7:01 PM, Kaho Ng <ngkaho1234@xxxxxxxxx> wrote: > I am trying to investigate how freelist allocator in xfs interacts > with freespace B+Tree allocator. > First I prepared a patch > <https://gist.github.com/22ffca35929e67c08759b057779b7566> on > linux-source/fs/xfs/libxfs/xfs_alloc.c to print debugging messages > (The kernel version used is linux-3.10.0-327.22.2.el7). > Then, I wrote a simple utility > <https://gist.github.com/992364ceca984d3f14099ec94aaacd9d> to make > TONS of > holes in a filesystem by calling fallocate() to punch holes in a file > that is almost as large as the volume size. > > I created an XFS filesystem image by the following steps: > 1. fallocate -l 80G /mnt/disk2/xfs > 2. mkfs.xfs -f -d agcount=1 /mnt/disk2/xfs > > Then I created a large file by fallocate: > fallocate -l 85823746048 /mnt/test/abc > > which left only 4 blocks available in the volume finally: > /dev/loop0 20961280 20961276 4 100% /mnt/test > > The result of xfs_bmap against /mnt/test/abc: > /mnt/test/abc: > EXT: FILE-OFFSET BLOCK-RANGE AG AG-OFFSET TOTAL FLAGS > 0: [0..167624503]: 83000..167707503 0 (83000..167707503) 167624504 10000 > > After that, I used the hole-punching utility above to create holes on > the files, and captured the output of kmsg. > > When reading the log output > <https://gist.github.com/890076405e1c13c0a952a579e25e6afe> , I > realised that there is no B+Tree split > triggered by xfs_alloc_fix_freelist() when calling xfs_free_extent(). > Isn't B+Tree split possible in by-size B+Tree even when truncating a > longer freespace record to shorter one? But what I found in the log is > only a few tree shrinks... And when reading the source code of > freespace allocator I found that a B+Tree growth in this case is > impossible at least... _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
